This invention relates to evacuated insulation panels, a method for the production thereof and their use for thermal insulation purposes.
Evacuated insulation panels and methods for their production are known.
Evacuated insulation panels having a reduced internal pressure are known for various uses including use in refrigeration appliances where they greatly enhance the degree of thermal insulation within the cabinet of the appliance.
Such evacuated insulation panels generally comprise a low thermal conductivity filler material and a vessel formed of a gastight film enveloping said filler, the whole being evacuated to an internal pressure of about 5 mbar or less and then hermetically sealed. Besides insulation the filler has also the function of supporting the skin of the vessel so that it does not collapse when it is evacuated.
Known filler materials for use in such evacuated insulation panels include finely divided inorganic powders such as fumed silica, silica dust, precipitated silica, precipitated silica/fly ash mixtures, alumina, fine perlite and fiberglass. It has also been proposed, in Japanese Patent Application Kokai No. 133870/82, to use organic foamed materials having open cells as the core material in evacuated insulation panels, for example, open celled rigid polyurethane foam (see European Patent Publications Nos 0498628 and 0188806).
WO 97/27986 describes a method to improve the thermal insulation properties of an evacuated insulation panel filled with an open celled rigid insulating foam. This method involves compressing the open celled rigid foam to a thickness of 40 to 90% of its initial thickness prior to compression, enclosing the compressed foam in a receptacle, evacuating the receptacle to a partial or near total vacuum and hermetically sealing the receptacle. The insulating performance of the foam on a per unit thickness is enhanced by compression of the foam.
However evacuated panels compressed according to the method described in WO 97/27986 are not completely flat and the surface of the panels shows a lot of wrinkles. This can lead to air entrapments when the panel is foamed-in-place in a refrigerator cabinet.
Therefore it is an object of the present invention to provide an evacuated insulation panel comprising an open celled insulating foam having improved thermal insulation properties.
It is a further object of the present invention to provide an evacuated insulation panel comprising an open celled insulating foam, said panel having a very flat surface with zero or almost zero wrinkles.